A material mixer having an inclined rotatable drum for mixing animal feeds is disclosed by F. E. Buschbom in U.S. Pat. No. 4,797,004 issued Jan. 10, 1989. A longitudinal auger extended along a trough is located within the drum to carry feed from the lower end of the drum into a hopper or alternatively back into the mixing chamber. The conveyor trough is angularly tilted to regulate the volume of feed conveyed by the auger. The tilting of the trough does not break up bunches or accummulations of feed and therefor does not provide for an even flow of feed under all conditions. A chain and sprocket drive adjacent the lower end of the drum operates to concurrently rotate the auger and drum. In use the chain and sprocket drive places rotational or torque forces on the drum and frame supporting the drums. The rotational speeds of the auger and drum cannot be changed as the electric drive motor operably coupled to the chain and sprocket drive operates at a given speed. The mixer also has a flexible sealing belt biased into engagement with a fixed circular bead. The belt moves along the bead which causes wear on the belt. The belt can also bend outwardly which opens the seal allowing feed to flow out under the hopper. The hopper has a top opening to allow feeds to be placed into the mixer. The hopper does not accommodate a conveyor and trough assembly for directing large amounts of feed into the drum. The bulk material mixer of the invention overcomes the disadvantages of the material mixer disclosed in U.S. Pat. No. 4,797,004.